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| United States Patent |
5,780,399
|
|
Ishikawa
, et al.
|
July 14, 1998
|
Oil-soluble polyester, additive for lubricating oil, and lubricating oil
composition
Abstract
An oil-soluble polyester having a weight average molecular weight of 10,000
to 1 000,000, which is a polycondensate prepared by polycondensing the
following ingredients (A), (B) and (C):
(A) a divalent higher carboxylic acid ingredient,
(B) a divalent alcohol ingredient comprising a glycol represented by the
following formula:
HO--CH.sub.2 --CR.sup.1 R.sup.2 --CH.sub.2 --OH
wherein R.sup.1 and R.sup.2 represent a alkyl group, and the sum of carbon
numbers in R.sup.1 and R.sup.2 is at least three, and
(C) 0.1 to 15% by mole, based on the total of ingredients (A) and (B), of
at least one multi-valent ingredient selected from a carboxylic acid with
a valency of at least three and an alcohol with a valency of at least
three. This oil-soluble polyester is useful as an additive for a
lubricating oil.
| Inventors:
|
Ishikawa; Yoshihide (Himeji, JP);
Hasegawa; Shinsuke (Katou-gun, JP);
Miyamoto; Michio (Kakogawa, JP);
Kitahara; Shizuo (Kawaguchi, JP);
Shikatani; Yutaka (Kawasaki, JP);
Igarashi; Jinichi (Tokyo, JP)
|
| Assignee:
|
Nippon Zeon Co., Ltd. (Tokyo, JP);
Harima Chemicals, Inc. (Kakogawa, JP);
Nippon Oil Company, Ltd. (Tokyo, JP)
|
| Appl. No.:
|
598605 |
| Filed:
|
February 12, 1996 |
Foreign Application Priority Data
| Current U.S. Class: |
508/452; 508/455; 508/469; 508/481; 508/485; 508/486; 508/492; 508/496; 560/76; 560/81; 560/190; 560/199 |
| Intern'l Class: |
C10M 145/22 |
| Field of Search: |
508/452,469,455,481,485,486,492,496
44/398,386
560/76,81,190,199
|
References Cited
U.S. Patent Documents
| 3708522 | Jan., 1973 | LeSuer.
| |
| 4130494 | Dec., 1978 | Shaub.
| |
| 4609376 | Sep., 1986 | Craig et al.
| |
| 4956111 | Sep., 1990 | Wilburn et al.
| |
| 5314634 | May., 1994 | Kenbeek et al.
| |
| 5503762 | Apr., 1996 | Bongardt et al.
| |
| Foreign Patent Documents |
| 48-031186 | Apr., 1973 | JP.
| |
| 52-131982 | Nov., 1977 | JP.
| |
| 53-102307 | Sep., 1978 | JP.
| |
| 1311122 | Dec., 1989 | JP.
| |
Primary Examiner: Medley; Margaret
Attorney, Agent or Firm: Armstrong, Westerman, Hattori, Mcleland & Naughton
Claims
What is claimed is:
1. An oil-soluble polyester having a weight average molecular weight of
10,000 to 1,000,000, prepared by polycondensing the following components:
(A) a refined polymerized fatty acid comprising at least 60% by weight,
based on the weight of the polymerized fatty acid, of a dimer acid, or a
hydrogenated product of the polymerized fatty acid,
(B) a glycol represented by the following formula:
HO--CH.sub.2 --CR.sup.1 R.sup.2 --CH.sub.2 --OH
wherein R.sup.1 and R.sup.2 independently represent a linear or branched
alkyl group, and the sum of carbon numbers in R.sup.1 and R.sup.2 is at
least three, and
(C) 0.1 to 15 mole %, based on the total moles of components (A) and (B),
of at least one component selected from the group consisting of a
polycarboxylic acid and a polycarboxy alcohol.
2. The oil-soluble polyester according to claim 1, wherein the
polycarboxylic acid is at least one polycarboxylic acid selected from the
group consisting of trimellitic acid, tricarballylic acid, camphoronic
acid, trimesic acid and a trimer acid of polymerized fatty acid.
3. The oil-soluble polyester according to claim 1, wherein the polyhydric
alcohol is at least one polyhydric alcohol selected from the group
consisting of trimethylolethane, trimethylolpropane, trimethylolbutane,
glycerol, pentaerythritol, dipentaerythritol, sorbitol, glucose, mannitol,
sucrose and dextrose.
4. The oil-soluble polyester according to claim 1, wherein the equivalent
ratio of OH in the total alcohol to COOH in the total carboxylic acid is
in the range of 0.8 to 1.3.
5. The oil-soluble polyester according to claim 1, wherein the refined
polymerized fatty acid and polycarboxylic acid, in combination, have an
iodine value not larger than 50.
6. The oil-soluble polyester according to claim 1, which has an acid value
not larger than 10 mgKOH/g.
7. The oil-soluble polyester according to claim 1, which has a hydroxyl
value not larger than 30 mgKOH/g.
8. The oil-soluble polyester according to claim 1, which has an iodine
value not larger than 100.
9. A lubricating oil composition comprising the oil soluble polyester as
claimed in claim 1, and a base oil; the amount of the oil soluble
polyester being 0.1 to 40% by weight based on the weight of the
lubricating oil composition.
10. The lubricating oil composition according to claim 9, wherein the base
oil is a synthetic oil or a mineral oil, which has a kinematic viscosity
of 1 to 100 mm.sup.2 /sec at 100.degree. C.
11. The lubricating oil composition according to claim 9, which further
comprises a polymethacrylate.
12. The lubricating oil composition according to claim 11, wherein the
polymethacrylate is a dispersant polymethacrylate or a non-dispersant
polymethacrylate.
13. The lubricating oil composition according to claim 11, wherein the
polymethacrylate has a weight average molecular weight of 10,000 to
300,000.
14. The lubricating oil composition according to claim 11, wherein the
content of the sum of the oil-soluble polyester and the polymethacrylate
is in the range of 0.1 to 40% by weight based on the weight of the
lubricating oil composition.
15. The lubricating oil composition according to claim 11, wherein the
ratio of the oil-soluble polyester to the polymethacrylate is in the range
of 5/95 to 95/5 by weight.
16. An additive concentrate solution for lubricating oil comprising 100
parts by weight of an oil-soluble polyester as claimed in claim 1, and 10
to 500 parts by weight of a diluent oil.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to an oil-soluble polyester, an additive for a
lubricating oil, which comprises the oil-soluble polyester as an effective
ingredient, and a lubricating oil composition comprising the oil-soluble
polyester.
The oil-soluble polyester of the present invention is useful as a viscosity
index improver and a thickening agent, for a mineral lubricating oil and a
synthetic lubricating oil, and has an improved oxidation stability. The
lubricating oil composition having incorporated therein the oil-soluble
polyester is characterized as exhibiting a high viscosity index, an
enhanced shear stability and a lowered low-temperature viscosity.
(2) Description of the Related Art
As a viscosity index improver and a thickening agent, there can be
mentioned a polyalkyl methacrylate, polyisobutylene, an ethylene-propylene
copolymer, a styrene-diene block copolymer and a hydrogenated product
thereof. These polymeric materials are used usually as a linear polymer
having a weight average molecular weight of at least 50,000.
Of these polymeric materials, a polyalkyl methacrylate has good viscosity
index improving function and flow-point reducing function (i.e., a good
low-temperature viscosity lowering function). However, where a large
shearing force is imposed as used for a piston, a gear and a hydraulic
pressure pump, the main chain of the polyalkyl methacrylate is broken, and
the viscosity and viscosity index are undesirably reduced. Where the
polyalkyl methacrylate is incorporated, some lubricating oils tend to have
a precipitate during their use.
Polyisobutylene and an ethylene-propylene copolymer exhibit an enhanced
shear stability, but have a poor viscosity index improving function, i.e.,
exhibit a mere viscosity improving function.
Polyester viscosity index improvers are described in Japanese Unexamined
Patent Publication (JP-A) No. 46-31186, ibid. 52-131982 and ibid.
53-102367. More specifically, a viscosity improver comprising a
low-molecular-weight complete ester derived from a polyalkylenesuccinic
acid or a polymerized fatty acid and a dihydric alcohol is described in
JP-A 48-31186. This viscosity index improver has a relatively low
viscosity index improving function. A viscosity index improver composed of
a polyester derived from a polymerized fatty acid and a dihydric alcohol
and terminated with an aliphatic alcohol or a carboxylic acid is described
in JP-A 52-131982. This viscosity index improver exhibits a relatively low
viscosity index improving function and has poor low-temperature viscosity
characteristics. A lubricating oil composition comprising (1) a mineral
oil, (2) an ester of a polyhydric alcohol having a neopentyl structure
with a monocarboxylic acid, and (3) an ester prepared by polycondensing a
polyhydric alcohol having a neopentyl structure with a monocarboxylic acid
and simultaneously with a polycarboxylic acid is described in JP-A
53-102307. This lubricating oil composition has good thermal stability,
viscosity index and resistance to viscosity change under load, but the
ester ingredients (2) and (3) prepared from a monocarboxylic acid have a
low degree of polycondensation, as well known (for example, this fact is
described in Encyclopedia of Polymer Science and Technology, vol. 11,
"Polyester"). Therefore these ester ingredients have a poor viscosity
index improving effect.
Further, a viscosity index improver composed of a polyester prepared by
polycondensing a dimerized fatty acid with a glycol having no hydrogen
bound to the carbon atom at the .beta.-position and terminated with a
monohydric alcohol is described in JP-A 1-311122. This viscosity index
improver has a low degree of polycondensation, and thus, both the
viscosity index improving effect and the viscosity increasing effect are
poor.
To sum up, the conventional polyester viscosity index improvers generally
have a good shear stability, but, as regards the low-temperature viscosity
characteristics and viscosity index improving effect, there are increasing
demands for enhancing these characteristics.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an oil-soluble polyester
having good shear stability, viscosity index improving effect and
low-temperature viscosity characteristics.
Another object is to provide an additive for a lubricating oil, which
comprises an oil-soluble polyester having the beneficial properties.
Still another object is to provide a lubricating oil composition comprising
as an effective ingredient an oil-soluble polyester having the beneficial
properties.
In accordance with the present invention, there is provided an oil-soluble
polyester having a weight average molecular weight of 10,000 to 1,000,000,
which is a polycondensate prepared by polycondensing the following
ingredients (A), (B) and (C):
(A) a divalent higher carboxylic acid ingredient,
(B) a divalent alcohol ingredient comprising a glycol represented by the
following formula:
HO--CH.sub.2 --CR.sup.1 R.sup.2 --CH.sub.2 --OH
wherein R.sup.1 and R.sup.2 independently represent a linear or branched
alkyl group, and the sum of carbon numbers in R.sup.1 and R.sup.2 it at
least three, and
(C) 0.1 to 15% by mole based on the total of ingredients (A) and (B), of at
least one multi-valent ingredient selected from a carboxylic acid with a
valency of at least three and an alcohol with a valency of at least three.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
By the term "oil-soluble polyester" used herein we mean a polyester, a
solution of which exhibits a light transmittance of at least 90%,
preferably at least 95%, as measured by the following methods.
5 g of a polyester is placed in 95 g of a paraffinic mineral oil having a
kinematic viscosity of 4.1 mm.sup.2 /sec at 100.degree. C. a viscosity
index of 101, an aniline point of 97.8.degree. C. and a pour point of
-15.degree. C. and the mixture is stirred in a nitrogen atmosphere at
100.degree. C. for one hour to dissolve the polyester. Then the resulting
solution is cooled to room temperature 120.degree. C.). The cooled
solution is allowed to stand at 20.degree. C. in a thermostatically
controlled chamber for 24 hours, The solution is again stirred, and the
light transmittance (%) is measured by a turbidity meter (Model "ANA-14S"
supplied by TOKYO PHOTOELECTRIC CO., LTD.). A tungsten incandescent
electric lamp (6 V, 6 A) is used as a light source, and 20 mm square glass
cell is used as a cell. The light transmittance as measured in the state
where the shutter is closed is regarded as zero, and the light
transmittance of the paraffinic mineral oil used is regarded as 100%.
As examples of the divalent higher carboxylic acid used in the present
invention, there can be mentioned linear, branched, cyclic and aromatic
divalent carboxylic acids having usually at least 20 carbon atoms. These
divalent carboxylic acids may be used either alone or in combination of
these, those are preferable which contain at least 60% by weight of a
branched divalent carboxylic acid. Preferably the branched divalent
carboxylic acid is at least one carboxylic acid selected from
alkylenesuccinic acids and dimer acids of polymerized fatty acids. The
most preferable branched divalent carboxylic acid is a dimer acid of a
polymerized fatty acid.
A polymerized fatty acid is a polymerization product of higher fatty acids.
More specifically, a polymerized fatty acid is the generic name of
polymerized acids prepared by polymerizing fatty acids having usually 8 to
24, preferably 16 to 20 carbon atoms, which are saturated or have at least
one unsaturation, or fatty acid ester derivatives thereof. Commercially
available polymerized fatty acids are polymerization products of oleic
acid, linolic acid, ricinoleic acid, eleostearic acid and other fatty
acids, which contain dimer acids as the principal ingredients, and
polymeric acids comprising trimer or more polymers and monomeric acids as
minor ingredients. Structural analysis of polymerized fatty acids are
described in D. H. Macmahon et al; J. Am Oil. Chem. Soc., vol. 51, 522
(1974). The polymerized products can be fractionated into a plurality of
polymerized fatty acids having different contents of the respective
ingredients by distillation or extraction with a solvent.
Hydrogenated polymerized fatty acids having an enhanced thermal stability
can be prepared by hydrogenating the unsaturated carbon-carbon bonds
remaining in the polymerized fatty acids.
Unrefined polymerized fatty acids, refined polymerized fatty acids and
hydrogenated polymerized fatty acids can be used in the present invention.
Refined polymerized fatty acids containing at least 60% by weight,
especially at least 95% by weight, of dimer acids, and hydrogenation
products thereof are preferable.
A polyalkylenesuccinic acid is represented by the following formula (1):
##STR1##
wherein R represents a polymer chain of a lower alkylene which is at least
one alkylene preferably selected from ethylene, propylene and butylene.
The polymer chain preferably has a polymerization degree of 10 to 300.
The divalent alcoholic ingredient (B) used in the present invention
comprises a glycol having no hydrogen atom at the .beta.-position, which
is represented by the formula:
HO--CH.sub.2 --CR.sup.1 R.sup.2 --CH.sub.2 --OH
wherein R.sup.1 and R.sup.2 independently represent a linear or branched
alkyl group, and the sum of carbon numbers in R.sup.1 and R.sup.2 is at
least 3, preferably at least 4 and more preferably at least 5. The
permissible largest number of the sum of carbon numbers in R.sup.1 and
R.sup.2 is not particularly limited, but is preferably 20, more preferably
10. When the sum of carbon numbers in R.sup.1 and R.sup.2 is too small,
the oxidation stability becomes low. In contrast, when the sum of carbon
numbers in R.sup.1 and R.sup.2 is too large, the reactivity with
carboxylic acid ingredients becomes poor.
As examples of the linear or branched alkyl group, there can be mentioned
methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl,
t-butyl, n-pentyl, n-hexyl, n-octyl and 2,2-dimethylhexyl. Of these, n- or
t-alkyl groups having no methine proton such as ethyl, n-propyl, n-butyl,
t-butyl, n-hexyl and 2,2-dimethylhexyl are preferable. Especially, n-alkyl
groups such as ethyl, n-propyl, n-butyl and n-hexyl are more preferable.
The glycol of the above formula having no hydrogen at the .beta.-position
is synthesized by a method similar to the method described in JP-A
3-161452, i.e., a method comprising a combination of an aldol condensation
mechanism with a Cannizzaro reaction mechanism. For example,
dimethylol-heptane is synthesized from n-butylaldehyde, sodium hydroxide
and formaldehyde. AS specific examples of the glycol, there can be
mentioned 2-butyl-2-ethyl-1,3-propane-diol,
2-pentyl-2-propyl-1,3-propanediol, 2-propyl-2-ethyl-1,3-propanediol,
2,2-diethyl-1,3-propanediol and 2-ethyl-2-methyl-1,3-propanediol.
A small amount of at least one multi-valent ingredient (C) selected from
carboxylic acids with a valency of at least three and alcohols with a
valency of at least three is used in combination with the divalent higher
carboxylic acid (A) and the divalent alcohol ingredient comprising the
glycol having no hydrogen atom at the .beta.-position in the present
invention.
The effect of a viscosity index improvement generally has a positive
relationship with the molecular weight of polymer added. The higher the
molecular weight of a polyester viscosity index improver, the higher the
viscosity index. Therefore, it is essential to obtain a high polymer when
divalent higher carboxylic acid ingredients such as a polymerized fatty
acid and a polyalkylenesuccinic acid are polycondensed with divalent
alcohol ingredients. The molecular weight of a polyester varies depending
upon the particular OH/COOH ratio. Namely, if the OH/COOH ratio
(equivalent ratio) is 1.0, the molecular weight will increase to an
unlimited extent. However, when the OH/COOH ratio is 1.0, the rate of
reaction is reduced with a progress of the polycondensation reaction, and
thus, a substantial long period of time is required for the completion of
reaction. This is not advantageous from an economical viewpoint.
In the polycondensation of the divalent higher carboxylic acid ingredient
such as a dimer acid with the divalent alcohol ingredient, the molecular
weight of the obtained polymer can be effectively increased by the
incorporation of a small amount of a trihydric alcohol or an alcohol with
a larger valency in the divalent alcohol ingredient, or a small amount of
a carboxylic acid with a valency of at least three in the divalent higher
carboxylic acid ingredient.
The carboxylic acid with a valency of at least three is not particularly
limited provided that it has at least three carboxyl groups. As specific
examples of the carboxylic acid, there can be mentioned trimellitic acid,
tricarballytic acid (1,2,3-propanetricarboxylic acid), camphoronic acid
(2,3-dimethylmethane-1,2,3-tricarboxylic acid), trimesic acid
(1,3,5-benzenetricarboxylic acid), trimer acids of polymerized fatty
acids, and hydrogenation products thereof. Of these, trimesic acid, trimer
acids of polymerized fatty acids, and hydrogenation products thereof are
preferable. Trimer acids of polymerized fatty acids, and hydrogenation
products thereof are most preferable.
The alcohol with a valency of at least three is not particularly limited
provided that it has at least three hydroxyl groups. As specific examples
of the alcohol, there can be mentioned trimethylolethane
trimethylolpropane, tri-methylolbutane, glycerol, pentaerythritol,
dipentaerythritol, sorbitol, glucose, mannitol, sucrose and dextrose. Of
these, trimethylolethane, trimethylolpropane, glycerol, pentaerythritol,
dipentaerythritol and sorbitol are preferable.
The equivalent ratio of OH in the total alcohol ingredient to COOH in the
total carboxylic acid ingredient is preferably in the range of 0.8 to 1.3,
more preferably 0.9 to 1.1 and most preferably approximately 1.0. The
amount of the carboxylic acid with a valency of at least three is not
larger than 15% by mole based on the total weight of the carboxylic acid
ingredients. The amount of the alcohol with a valency of at least three is
not larger than 15% by mole based on the total weight of the alcohol
ingredients. The amount of the multi-valent ingredient (C) (i.e., the
carboxylic acid with a valency of at least three and/or the alcohol with a
valency of at least three) is in the range of 0.1 to 15% by mole,
preferably 1 to 10% by mole, based on the total of the divalent higher
carboxylic acid ingredient and the divalent alcohol ingredient (B). If the
amount of the carboxylic acid with a valency of at least three and/or the
alcohol with a valency of at least three is too large, the
polycondensation reaction is difficult to control.
Provided that the object of the present invention is achieved, carboxylic
acids other than the divalent higher carboxylic acid ingredient (A) and
the carboxylic acid with a valency of at least three (C) can be used in
combination with the ingredients (A) and (B). As examples of such
carboxylic acids, there can be mentioned lower dicarboxylic acids such as
succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid,
sebacic acid, phthalic acid and terephthalic acid; and monocarboxylic
acids including saturated fatty acids such as 2-methylpropane acid,
iso-octylic acid, isononanoic acid, lauric acid, myristic acid, palmitic
acid, stearic acid, isostearic acid and arachic acid, and unsaturated
acids such as linolic acid, oleic acid and elaidic acid. The maximum
permissible amount of these carboxylic acids is generally not larger than
10% by mole based on the total carboxylic acid ingredients.
The total carboxylic acid ingredients have an iodine value of preferably
not larger than 50, more preferably not larger than 20. Where the iodine
value is low, the oxidation stability of the resulting polyester is
enhanced. In this respect, hydrogenation products of polymerized fatty
acids including diner acids, and hydrogenation products of polymerized
fatty acids including trimer acids are preferable in the present
invention. Hydrogenation of polymerized fatty acids can be conducted by a
known method, for example described in D. H. Macmahon et al: J. Am. Chem.
Soc., vol. 51, p522 (1974).
Provided that the object of the present invention is achieved, monohydric
alcohols and dihydric alcohols other than the divalent alcohol ingredient
comprising a glycol having no hydrogen atom, at the .beta.-position (B)
can be used in combination with the ingredient (B) and the alcohol with a
valency of at least three (C). As specific examples of the dihydric
alcohols, there can be mentioned alkanediols such as ethylene glycol,
propylene glycol, 1,2-butanediol, 1,4-butanediol, 1,6-hexanediol,
3-methyl-1,5-pentanediol, neopentyl glycol and dimer diol, polyoxyalkylene
glycols such as polyethylene glycol, polypropylene glycol and
polyoxyethylene-polypropylene glycols, including oligo oxyalkylene glycols
such as diethylene glycol, dipropylene glycol and triethylene glycol, and
polyesterdiols. As specific examples of the monohydric alcohols, there can
be mentioned neopentyl alcohol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol,
2,3,3-trimethyl-2-butanol, 1-decanol and nonyl alcohol.
The polycondensation of the above-mentioned ingredients (A), (B) and (C)
and other optional carboxylic acid ingredient and alcohol ingredient can
be conducted by the conventional procedure. Usually the polycondensation
is carried out at a temperature of 150.degree. to 280.degree. C. in an
inert gas atmosphere. If desired, a non-aqueous organic solvent forming an
azeotrope with water such as toluene or xylene is used as the reaction
medium. The reaction may be carried out under a reduced pressure. In the
polycondensational esterification, an esterification catalyst is used,
which includes for example, paratoluenesulfonic acid, sulfuric acid, a
trifluoroboron complex, phosphoric acid hydrochloric acid, potassium
acetate zinc stearate, zinc, titanium, and metal oxides such as tin oxide
and titanium oxide. Of these, metal oxides are preferable in view of the
oxidation stability.
The thus-prepared oil-soluble polyester has a weight average molecular
weight (Mw) of 10,000 to 1,000,000, preferably 15,000 to 600,000 and more
preferably 20,000 to 400,000. The most preferable molecular weight is
40,000 to 200,000. If the Mw is too small, the effect of viscosity index
improvement is poor. In contrast, if the Mw is too large, the shear
stability and solubility in a mineral oil and other lubricating oils are
reduced.
The oil-soluble polyester of the present invention can be used either alone
or as a mixture comprised of at least two of the polyesters or a mixture
comprised of at least one of the polyester and at least one other
polyester which includes, for example, an ordinary polyester made from a
dicarboxylic acid and a dihydric alcohol. The molecular weight of the
polyester used in combination with the polyester of the present invention
can be appropriately chosen depending upon the intended use and the kind
of the polyester used. For example, if a polyester having a weight average
molecular weight of 10,000 to 50,000 is used in combination with a
polyester having a weight average molecular weight of 50,000 to 1,000,000,
the resulting polyester composition has good and balanced effect of
viscosity index improvement and shear stability.
The oil-soluble polyester of-the present invention has an acid value of not
larger than 10 mgKOH/g, preferably not larger than 5 mgKOH/g, and more
preferably not larger than 3 mgKOH/g. If the acid value is too large, a
problem of corrosion arises.
The oil-soluble polyester of the present invention has a hydroxyl value of
not larger than 30 mgKOH/g, and preferably not larger than 10 mgKOH/g. If
the hydroxyl value is too large, the solubility in a lubricating oil
becomes poor.
The oil-soluble polyester of the present invention preferably has an iodine
value of not larger than 100 in view of the oxidation stability, The
iodine value is more preferably not larger than 20 and most preferably not
larger than 10.
Where the oil-soluble polyester of the present invention is used as
additives for a lubricating oil, such as a viscosity index improver and a
thickening agent, the polyester is used as it is or, to enhance the
handling properties, used in the form of a solution in a diluent. The
diluent used is not particularly limited, but is usually a mineral oil or
a synthetic oil which is usually used as a solvent of general purpose or a
lubricating oil and which has a boiling point of 70.degree. to 700.degree.
C., preferably 120.degree. to 650.degree. C. and more preferably
150.degree. to 600.degree. C.
The mineral oil used may be a paraffinic, naphthenic or aromatic solvent
fraction or lubricating oil fraction, which is prepared by refining a
solvent fraction obtained by normal pressure distillation or reduced
pressure distillation of crude oil. The refining is usually carried out by
a combination of refining procedures such as hydrogenation refining,
sulfuric acid washing and china clay treatment. As examples of the mineral
oil, there can be mentioned aromatic hydrocarbons such as benzene, toluene
and xylene, petroleum solvents such as petroleum benzine, rubber solvent,
soybean oil solvent, ligroin, mineral spirit, cleaning solvent and
stoddard solvent, and fractions of mineral oil such as gasoline fraction,
kerosine fraction, gas oil fraction and lubricating oil fraction.
As examples of the synthetic oil used, there can be mentioned
low-molecular-weight .alpha.-olefin oligomers obtained by polymerization
of an olefin such as ethylene, propylene, butene, isobutylene, 1-octene or
1-decene, or a mixture thereof; synthetic isoparaffin or hydrogenated
poly-.alpha.-olefins, prepared by hydrogenating double bonds in
poly-.alpha.-olefins; hard-type alkylbenzenes prepared by alkylating
benzene with a propylene oligomer, or soft-type alkylbenzenes obtained by
alkylating benzene with chlorinated paraffin prepared by chlorinating
normal paraffin or with a normal olefin prepared by dehydrogenating normal
paraffin separated from kerosine; alkylnaphthalenes obtained by alkylating
naphthalene with an olefin or chlorinated paraffin; diesters such as
ditridecyl glutarate, di-2-ethylhexyl adipate, dilsodecyl adipate,
ditridecyl adipate and di-2-ethylhexyl sebacate; polyesters such as
trimellitate; polyol-esters such as trimethylolpropane caprilate,
trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate and
pentaerythritol pelargonate; polyoxyalkylene glycols; dialkyl diphenyl
ethers; and polyphenyl ethers.
These mineral oils and synthetic oils may be used either alone or in
combination.
Where the oil-soluble polyester is used as an additive for a lubricating
oil, in the form of a solution in a diluent, the amount of the diluent
used is not particularly limited, but is usually in the range of 10 to 500
parts by weight per 100 parts by weight of the oil-soluble polyester.
By the incorporation of the oil-soluble polyester as it is or as a solution
in a diluent, in a base oil, a lubricating oil composition exhibiting
improved viscosity-temperature characteristics (i.e., viscosity index and
low-temperature characteristics) and shear stability.
The base oil used is not particularly limited, and mineral oils and
synthetic oils conventionally used as base oils of lubricating oils can be
used.
As examples of the mineral base oil for a lubricating oil, there can be
mentioned those which are prepared by refining a paraffinic or naphthenic
lubricating oil fraction obtained by normal pressure distillation or
reduced pressure distillation of crude oil. The refining is usually
carried out by a combination of refining procedures selected from
bituminous substance-removal with a solvent, extraction with a solvent,
hydrogenating cracking, dewaxing with a solvent catalytic dewaxing,
hydrogenating refining, washing with sulfuric acid, and china clay
treatment.
As examples of the synthetic base oil for a lubricating oil used, there can
be mentioned low-molecular-weight .alpha.-olefin oligomers obtained by
polymerization of an olefin such as ethylene, propylene, butene,
isobutylene, 1-octene or 1-decene, or a mixture thereof; synthetic
isoparaffin or hydrogenated poly-.alpha.-olefins, prepared by
hydrogenating double bonds in poly-.alpha.-olefins; hard-type
alkylbenzenes prepared by alkylating benzene with a propylene oligomer, or
soft-type alkylbenzenes obtained by alkylating benzene with chlorinated
paraffin prepared by chlorinating normal paraffin or with a normal olefin
prepared by dehydrogenating normal paraffin separated from kerosine;
alkylnaphthalenes obtained by alkylating naphthalene with an olefin or
chlorinated paraffin; diesters such as ditridecyl glutarate,
di-2-ethylhexyl adipate, dilsodecyl adipate, ditridecyl adipate and
di-2-ethylhexyl sebacate; polyesters such as trimellitate; polyol-esters
such as trimethylolpropane caprilate, trimethylolpropane pelargonate,
pentaerythritol 2-ethylhexanoate and penta-erythritol pelargonate;
polyoxyalkylene glycols; dialkyl diphenyl ethers; and polyphenyl ethers.
These base oils and synthetic oils may be used either alone or in
combination. The base oil may also be used as a diluent for diluting the
oil-soluble polyester of the present invention when the polyester is used
as an additive for a lubricating oil.
The viscosity of the base oil used is not particularly limited, but the
kinematic viscosity at 100.degree. C. is usually 1 to 100 mm.sup.2 /s,
preferably 2 to 50 mm.sup.2 /s and more preferably 2 to 20 mm.sup.2 /s.
The amount of the oil-soluble polyester incorporated in a base oil for a
lubricating oil is not particularly limited, but is usually 0.1 to 40% by
weight, preferably 0.3 to 30% by weight and more preferably 0.5 to 20% by
weight, based on the total weight of the lubricating oil composition.
The incorporation of the oil-soluble polyester in a base oil results in a
lubricating oil composition exhibiting improved viscosity-temperature
characteristics (i.e., viscosity index and low-temperature
characteristics) and shear stability, at mentioned above. When a
polymethacrylate is further added in the lubricating oil composition, the
viscosity-temperature characteristics (i.e., viscosity index and
low-temperature characteristics) are further enhanced and the oxidation
stability is improved, while the improved shear stability is maintained.
As the polymethacrylate, a non-dispersant polymethacrylate, a dispersant
polymethacrylate and a mixture thereof are used.
As typical examples of the non-dispersant polymethacrylate, there can be
mentioned polymers of an alkyl methacrylate represented by the following
formula (2):
##STR2##
wherein R.sup.3 represents an alkyl group having 1 to 24 carbon atoms,
preferably 1 to 18 carbon atoms. As specific examples of the alkyl group,
there can be mentioned methyl, ethyl, propyl, butyl, pentyl, hexyl,
heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,
pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl,
heneicosyl, docosyl, tricosyl and tetracosyl groups. These alkyl groups
may be either linear or branched.
The polymethacrylate may be a homopolymer of an alkyl methacrylate of the
formula (2) or a copolymer (random copolymer, block copolymer or
alternating copolymer) of two or more of alkyl methacrylates of the
formula (2). In view of excellent viscosity-temperature characteristics, a
copolymer, especially a random copolymer is preferable. The
non-dispersion-type polymethacrylate may be used either alone or in
combination.
As examples of the dispersant polymethacrylate, there can be mentioned
copolymers of a nitrogen-free ethylenically unsaturated compound with a
nitrogen-containing methacrylate of the formula (3) shown below. The
nitrogen-free ethylenically unsaturated compound is at least one compound
selected from alkyl methacrylates of the formula (2) and aliphatic olefin
compounds having 2 to 18 carbon atoms, preferably 2 to 10 carbon atoms.
As specific examples of the aliphatic olefin compound having 2 to 18 carbon
atoms, there can be mentioned ethylene, propylene, butene, pentene,
hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene,
tetradecene, pentadecene, hexadecene, heptadecene and octadecene. These
aliphatic olefin compounds may be linear or branched, and may be an
.alpha.-olefin or an internal olefin. An .alpha.-olefin is preferable, and
a linear .alpha.-olefin is more preferable.
The nitrogen-containing methacrylate is represented by the following
formula (3):
CH.sub.2 .dbd.C(CH.sub.3)--COO--(R.sup.4).sub.a x (3)
wherein R.sup.4 is an alkylene group having 1 to 18 carbon atoms,
preferably 1 to 6 carbon atoms, a is an integer of 0 or 1, and X is an
amine residue or a heterocyclic residue, which has 1 or 2 nitrogen atoms
and 0 to 2 oxygen atoms.
As specific examples of R.sup.4, there can be mentioned ethylene,
propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene,
decylene, undecylene, dodecylene, tridecylene, tetradecylene,
pentadecylene, hexadecylene, heptadecylene and octadecylene. These
alkylene groups may be either linear or branched.
As specific examples of X in the formula (3), there can be mentioned the
following groups: dimethylamino, diethylamino, dipropylamino,
dibutylamino,
##STR3##
As preferable examples of the nitrogen-containing methacrylate, there can
be mentioned the following compounds and mixtures thereof.
dimethylaminomethyl methacrylate ›CH.sub.2 .dbd.C(CH.sub.3)COOCH.sub.2
--N(CH.sub.3).sub.2 !, diethylaminomethyl methacrylate ›CH.sub.2
.dbd.C(CH.sub.3)COOCH.sub.2 --N(C.sub.2 H.sub.5).sub.2 !,
dimethylaminoethyl methacrylate ›CH.sub.2 .dbd.C(CH.sub.3)COO--CH.sub.2
CH.sub.2 --N(CH.sub.3).sub.2 !, diethylaminoethyl methacrylate ›CH.sub.2
.dbd.C(CH.sub.3)COO--CH.sub.2 CH.sub.2 --N(C.sub.2 H.sub.5).sub.2 !,
##STR4##
The dispersant polymethacrylate used is a copolymer of the nitrogen-free
monoethylenically unsaturated monomer with the nitrogen-containing
methacrylate. The ratio of the nitrogen-free monoethylenically unsaturated
monomer to the nitrogen-containing methacrylate is not particularly
limited, but is usually in the range of 70/30 to 99/1 by mole, preferably
80/20 to 98/2 by mole. The copolymerization process also not particularly
limited, and a process is usually employed wherein the monomeric
ingredients are copolymerized by a radical solution polymerization
procedure using a polymerization initiator such as benzoyl peroxide. The
copolymer may be a random copolymer, a block copolymer or an alternating
copolymer. In view of excellent viscosity-temperature characteristics, a
random copolymer is especially preferable.
Where the non-dispersant polymethacrylate or the dispersant
polymethacrylate is incorporated together with the oil-soluble polyester
in the lubricating oil composition of the present invention, the
non-dispersant polymethacrylate and the dispersant polymethacrylate may be
used alone, or as a mixture comprising the non-dispersant polymethacrylate
and the dispersant polymethacrylate at an optional ratio.
The weight average molecular weights of the non-dispersant polymethacrylate
and the dispersant polymethacrylate are not particularly limited, and is
usually in the range of 10,000 to 300,000, preferably 20,000 to 200,000.
Where both the oil-soluble polyester and the polymethacrylate are
incorporated in the lubricating oil composition of the present invention,
the total amount of the oil-soluble polyester and the polymethacrylate are
usually in the range of 0.1 to 40% by weight, preferably 0.3 to 30% by
weight and more preferably 0.5 to 20% by weight, based on the total weight
of the lubricating oil composition. The ratio of the oil-soluble polyester
to the polymethacrylate is not particularly limited, and is usually in the
range of 5/95 to 95/5 by weight, preferably 20/80 to 80/20 by weight.
One or more conventional additives can be added into the lubricating oil
composition of the present invention to modify the lubricating oil
composition.
As examples of the additives used, there can be mentioned antioxidants
including hindered phenolic antioxidants such as 2,6-di-t-butyl-p-cresol
and 4,4'-methylenebis-2,6-di-t-butylphenol, amine antioxidants such as
alkyldiphenylamine and .alpha.-naphthylamine, sulfur-containing
antioxidants, zinc dithiophosphate antioxidants, zinc dithiocarbamate
antioxidants and phenothiazine antioxidants; rust preventives such as an
alkenylsuccinic acid, an alkenylsuccinic acid ester, a polyhydric alcohol
ester, an alkaline earth metal petroleum sulfonate, an alkaline earth
metal alkylbenzenesulfonate and an alkaline earth metal
dinonylnaphthalenesulfonate; metal-deactivating agents such as
benzotriazole and thiadiazole; abrasion preventives including
high-pressure abrasion preventives, such as a phosphate ester, a phosphite
ester, sulfurized fatty oil, a sulfide, a sulfophosphorized polybutene, a
sulfophosphorized ester and zinc thiophosphate; lubricants such as a fatty
acid, an aliphatic amine, an aliphatic amine salt, a fatty acid amide,
molybdenum dithiophosphate and molybdenum dithiocarbamate;
metal-containing cleaning agents such as an alkaline earth metal
sulfonate, an alkaline earth metal phenate, an alkaline earth metal
salicylate and an alkaline earth metal phosphonate; ash-free dispersants
such as an alkenylsuccinic acid imide, an alkenylsuccinic acid ester,
benzylamine, polybutenylamine and an amidation product thereof; viscosity
index improvers and pour point depressant, such as polyisobutylene, an
ethylene-propylene copolymer, a hydrogenated styrene-butadiene copolymer,
a hydrogenated styrene-isoprene copolymer, styrenic polyesters, an
ethylenevinyl acetate copolymer and an esterified styrene-maleic anhydride
copolymer; and anti-foaming agents such as methylsilicone, fluorosilicone
and a polyacrylate.
The amount of these additives is not particularly limited, but is usually
0.0005 to 1% by weight in the case of an antifoaming agent, 1 to 30% by
weight in the case of a viscosity index improver, 0.005 to 1% by weight in
the case of a metal-deactivating agent and 0.1 to 15% by weight in the
case of the other additives, based on the total weight Of the lubricating
oil composition.
The lubricating oil composition of the present invention containing the
oil-soluble polyester and an optional polymethacrylate is advantageously
used as lubricating oils, to which a high viscosity index is required, and
which include, for example, internal combustion engine oils such as
gasoline engine oil, diesel engine oil and gas engine oil; automobile gear
oils such as automatic transmission fluid, manual transmission fluid and
differential oil; automobile hydraulic fluids such as shock-absorber oil
and active suspension fluid. Further, the lubricating oil composition is
used as two-cycle engine oil, marine oil, turbine oil, industrial gear
oil, compressor oil, refrigerator oil, cutting oil, metal working oils
such as rolling oil, pressing oil, forging oil, milling oil, drawing oil
and punching oil, metal-processing oils such as heat-treating oil and
electrical discharge machining oil, sliding guide way lubricant, bearing
oil, rust preventive oil and heat transfer oil.
The invention will now be specifically described by the following examples
that by no means limit the scope of the present invention.
In the examples, % and parts are by weight unless otherwise specified.
The hydroxyl value, acid value and iodine value of polyesters were
determined according to the following standards described in "Standard
Methods for the Analysis of Oils, Fats and Derivatives" (Japan Oil
Chemists' Society)
Hydroxyl value 2. 4. 9. 2-83
Acid value 2. 4. 1-83
Iodine value 2. 4. 5-71
EXAMPLE 1
A 1,000 ml four-necked flask equipped with a stirrer, a thermometer, a
reflux condenser, a water-separating tube and a nitrogen gas supplying
tube was charged with 570.4 g of hydrogenated polymerized fatty acid
(hydrogenated product of "HARIDIMER 300" supplied by Harima Chemicals,
Inc.) having an iodine value of 6 and an acid value of 195 mgKoH/g and
containing 0.5% of monomer acid, 97.0% of dimer acid and 2.5% of trimer
acid, 165.2 g of 2-butyl-2-ethyl-1,3-propanediol and 0.26 g of
monobutyltin oxide (catalyst) (OH/COOH equivalent ratio=1.04)
Nitrogen gas was blown into the flask while the content was stirred, and
the temperature was elevated to 100.degree. C. While water produced during
the reaction was removed, the temperature of the reaction mixture was
elevated from 100.degree. C. to 260.degree. C. over a period of 6 hours.
Then the reaction was continued for 10 hours at 260.degree. C. while
dehydration was conducted. The thus-obtained polyester (hereinafter
abbreviated to "polyester 1") had a weight average molecular weight of
45,000, an acid value of 0.2 mgXOH/g and a hydroxyl value of 3.4 mgKOH/g.
Light transmission of its solution in paraffinic mineral oil was 98%.
EXAMPLE 2
A 1,000 ml four-necked flask equipped with a stirrer, a thermometer, a
reflux condenser, a water-separating tube and a nitrogen gas supplying
tube was charged with 474.4 g of hydrogenated polymerized fatty acid (the
same as that used in Example 1), 119.6 g of hydrogenated polymerized fatty
acid (hydrogenated product of "HARIDIMER 270S" supplied by Harima
Chemicals, Inc.) having an iodine value of 7.5 and an acid value of 193
mgKOH/g and containing 0.5% of monomer acid, 80.5% of dimer acid and 19.0%
of trimer acid, 143.1 g of 2-butyl-2-ethyl-1,3-propanediol and 0.26 g of
monobutyltin oxide (catalyst) (OH/COOH equivalent ratio=1.05).
Nitrogen gas was blown into the flask while the content was stirred, and
the temperature was elevated to 100.degree. C. While water produced during
the reaction was removed, the temperature of the reaction mixture was
elevated from 100.degree. C. to 260.degree. C. over a period of 6 hours.
Then the reaction was continued for 10 hours at 260.degree. C. while
dehydration was conducted. The thus-obtained polyester (hereinafter
abbreviated to "polyester 2") had a weight average molecular weight of
83,000, an acid value of 0.2 mgKOH/g and a hydroxyl value of 2.5 mgKOH/g.
Light transmission of its solution in paraffinic mineral oil was 98%.
EXAMPLE 3
A 1,000 ml four-necked flask equipped with a stirrer, a thermometer, a
reflux condenser, a water-separating tube and a nitrogen gas supplying
tube was charged with 573.5 g of hydrogenated polymerized fatty acid (the
same as that used in Example 1), 157.9 g of 2-butyl-2-ethyl-1,
3-propanediol, 5.4 g of trimethylolpropane and 0.26 g of monobytyltin
oxide (catalyst) (OH/CCOH equivalent ratio=1.05).
Nitrogen gas was blown into the flask while the content was stirred, and
the temperature was elevated to 100.degree. C. While water produced during
the reaction was removed, the temperature of the reaction mixture was
elevated from 100.degree. C. to 240.degree. C. over a period of 6 hours.
Then the reaction was continued for 10 hours at 240.degree. C. while
dehydration was conducted. The thus-obtained polyester (hereinafter
abbreviated to "polyester 3") had a weight average molecular weight of
105,000, an acid value of 0.2 mgKOH/g and a hydroxyl value of 2.1 mgKOH/g.
Light transmission of its solution in paraffinic mineral oil was 97%.
Comparative Example 1
A 1,000 ml four-necked flask equipped with a stirrer, a thermometer, a
reflux condenser a water-separating tube and a nitrogen gas supplying tube
was charged with 620.0 g of hydrogenated polymerized fatty acid (the same
as that used in Example 1, 118.0 g of 2,2-dimethyl-1,3-propanediol, and
0.26 g of monobutyltin oxide (catalyst) (OH/COOH equivalent ratio=1.05).
Nitrogen gas was blown into the flask while the content was stirred, and
the temperature was elevated to 100.degree. C. While water produced during
the reaction was removed, the temperature of the reaction mixture was
elevated from 100.degree. C. to 240.degree. C. over a period of 6 hours.
Then the reaction was continued for 10 hours at 240.degree. C. while
dehydration was conducted. The thus-obtained polyester (hereinafter
abbreviated to "polyester A") had a weight average molecular weight of
41,000, an acid value of 0.2 mgKOH/g and a hydroxyl value of 3.0 mgKOH/g.
Comparative Example 2
A 1,000 ml four-necked flask equipped with a stirrer, a thermometer, a
reflux condenser, a water-separating tube and a nitrogen gas supplying
tube was charged with 575.4 g of hydrogenated polymerized fatty acid (the
same as that used in Example 1), 140.0 g of dipropylene glycol, 3.5 g of
triymethylolpropane and 0.26 g of monobutyltin oxide (catalyst) (OH/COOH
equivalent ratio=1.05).
Nitrogen gas was blown into the flask while the content was stirred, and
the temperature was elevated to 100.degree. C. While water produced during
the reaction was removed, the temperature of the reaction mixture was
elevated from 100.degree. C. to 240.degree. C. over a period of 6 hours.
Then the reaction was continued for 10 hours at 240.degree. C. while
dehydration was conducted. The thus-obtained polyester (hereinafter
abbreviated to "polyester B") had a weight average molecular weight of
83,000, an acid value of 0.4 mgKOH/g and a hydroxyl value of 2.8 mgKOH/g.
EXAMPLE 4
A 1,000 ml four-necked flask equipped with a stirrer, a thermometer, a
reflux condenser, a water-separating tube and a nitrogen gas supplying
tube was charged with 573.5 g of hydrogenated polymerized fatty acid (the
same as that used in Example 1), 130.3 g of 2,2-diethyl-1,3-propanediol,
5.4 g of trimethylolpropane and 0.26 g of monobutyltin oxide (catalyst)
(OH/COOH equivalent ratio=1.05).
Nitrogen gas was blown into the flask while the content was stirred, and
the temperature was elevated to 100.degree. C. While water produced during
the reaction was removed, the temperature of the reaction mixture was
elevated from 100.degree. C. to 240.degree. C. over a period of 6 hours.
Then the reaction was continued for 10 hours at 240.degree. C. while
dehydration was conducted. The thus-obtained polyester (hereinafter
abbreviated to "polyester 4") had a weight average molecular weight of
98,300, an acid value of 0.3 mgKOH/g and a hydroxyl value of 2.3 mgK.OH/g.
Light transmission of its solution in paraffinic mineral oil was 98%.
EXAMPLE 5
Using polyesters 1 to 4 and A and B, prepared in Examples 1 to 4 and
Comparative Examples 1 and 2, respectively, additives for a lubricating
oil (i.e., viscosity index improvers) I to VI were prepared. Namely, 50
parts of each polyester was blended with 50 parts of a diluent oil
("Neutral 100" refined paraffinic mineral oil having a kinematic viscosity
of 4.1 mm.sup.2 /s at 100.degree. C., a viscosity index of 101, an aniline
point of 97.8.degree. C. and a pour point of -15.degree. C.).
Each of the additives I to VI was added to the above-mentioned refined
paraffinic mineral oil to prepare a lubricating oil composition. In run 5
and run 6, a polymethacrylate was added in combination with the additive.
The amount of each additive was adjusted so that the resulting lubricating
oil composition had a kinematic viscosity of 10 mm.sup.2 /s at 100.degree.
C.
The viscosity index (VI) of the lubricating oil composition was measured
according to JIS K-2283. The shear stability of the lubricating oil
composition was expressed by viscosity reduction (%) which was determined
by measuring kinematic viscosity (mm.sup.2 /s) before and after
irradiation with ultrasonic wave and calculating the viscosity reduction
by the following formula according to JPS-5S-29-88.
Viscosity reduction (%)=›(V.sub.0 -V.sub.f)/V.sub.0 !.times.100 wherein
V.sub.0 is dynamic viscosity (mm.sup.2 /s) as measured before ultrasonic
irradiation, and V.sub.f is kinematic viscosity (mm.sup.2 /s) as measured
after ultrasonic irradiation. The results are shown in Table 1.
TABLE 1
__________________________________________________________________________
Comparative
Examples of Invention Examples
Run No.
1 2 3 4 6 7 1 2
__________________________________________________________________________
Polyester
1 2 3 4 1 3 A B
VI improver
I II III
IV I PMA*.sup.1
III PMA*.sup.2
V VI
Amount added
13.0
10.2
9.4
9.7 6.2 6.2
5.0 5.0
13.8
10.8
(%)
Viscosity
192
208
212
209 224 246 188
202
index (VI)
Shear stability
Viscosity
0.5
4.3
4.8
4.5 1.2 4.5 0.5
4.9
reduction
(40.degree. C.) (%)
Viscosity
0.1
4.0
5.0
4.6 1.3 4.5 0.5
5.0
reduction
(100.degree. C.) (%)
__________________________________________________________________________
*.sup.1 Nondispersant polymethacrylate (random copolymer of mixture of
alkyl methacrylates having 1 to 18 carbon atoms in the alkyl group, weigh
average molecular weight = 83,000)
*.sup.2 dispersant polymethacrylate (random copolymer of mixture of alkyl
methacrylates having 1 to 18 carbon atoms in the alkyl group) with
diethylaminoethyl methacrylate, weight average molecular weight = 100,000
content of nitrogencontaining monomer = 5 mole %)
EXAMPLE 6
Oxidation stability test (Indiana Stirring Oxidation Test, ISOT) of
internal combustion engine lubricating oil was conducted on the
lubricating oil compositions used in Example 5, according to JIS K-2514,
3-1 at 165.5.degree. C. for 24 hours. The results are shown in Table 2.
The viscosity ratio (V.sub.24 /V.sub.0) is the ratio of the kinematic
viscosity V.sub.24 as measured after the oxidation test to the kinematic
viscosity V.sub.0 as measured before the oxidation test. The measurement
of the kinematic viscosities was conducted at 40.degree. C. and
100.degree. C.
The viscosity index ratio (VI.sub.24 /VI.sub.0) is the ratio of the
viscosity index VI.sub.24 as determined after the oxidation test to the
viscosity index VI.sub.0 as determined before the oxidation test.
Lacquer degree was determined by comparison using a color scale stipulated
in JPI-5S15-80 according to JIS K-2514, 3-1. The results were expressed by
9 ratings. Rating 1 means that the coloration is minimum and the oxidation
stability is highest. Rating 9 means the coloration is maximum.
TABLE 2
______________________________________
Comparative
Example of Invention
Examples
Run No. 1 2 3 4 5 6 1 2
______________________________________
VI improver
I II III IV I III V VI
Viscosity
ratio V.sub.24 /V.sub.0
40.degree. C.
0.98 0.96 0.94 0.94 1.01 1.00 0.89 0.81
100.degree. C.
0.98 0.96 0.94 0.94 1.01 1.00 0.89 0.81
Viscosity
index ratio
VI.sub.24 /VI.sub.0
0.99 0.98 0.97 0.95 1.00 1.00 0.94 0.90
Acid value
0.1 0.1 0.1 0.1 0.1 0.1 0.95 1.35
increase
(mgKOH/g)
Lacquer 1 1 1 1 1 1 2 5
degree
______________________________________
As seen from Tables 1 and 2, the oil-soluble polyester of the present
invention is an additive for a lubricating oil which exhibits good
oxidation stability and viscosity index improvement. Where a
polymethacrylate is used in combination with the oil-soluble polyester,
the oxidation stability and viscosity index improvement are further
enhanced.
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